This invention relates to thermoplastic compositions of interpolymers of .alpha.-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers blended with one or more engineering thermoplastics.
The generic class of materials of .alpha.-olefin/hindered vinyl or vinylidene monomer substantially random interpolymers, including materials such as .alpha.-olefin/vinyl aromatic monomer interpolymers, and their preparation, are known in the art, such as described in EP 416 815 A2. These materials, such as ethylene/styrene interpolymers, offer a wide range of material structures and properties which makes them useful for varied applications, such as asphalt modifiers or as compatibilizers for blends of polyethylene and polystyrene, as described in U.S. Pat. No. 5,460,818.
The structure, thermal transitions and mechanical properties of substantially random interpolymers of ethylene and styrene containing up to about 50 mole percent styrene have been described (Y. W. Cheung, M. J. Guest; Proc. Antec '96 pages 1634-1637). These polymers are found to have glass transitions in the range -20.degree. C. to +35.degree. C., and show no measurable crystallinity above about 25 mole percent styrene incorporation, i.e. they are essentially amorphous.
Engineering thermoplastics are defined in the third edition of the Kirk-Othmer Encyclopedia of Science and Technology as thermoplastic resins, neat or unreinforced or filled, which maintain dimensional stability and most mechanical properties above 100.degree. C. and below 0.degree. C. Thermoplastics such as polycarbonate have found many uses because, in general, they combine a high level of heat resistance toughness and dimensional stability with good insulating and non-corrosive properties, and are easily molded. Polycarbonate does however, suffer from a tendency to craze and crack under the effect of contact with organic solvents such as gasoline. An undesirable result in polycarbonate which has crazed is that it is more likely to experience brittle rather than ductile failure.
This disadvantage has been somewhat relieved by the practice of blending polycarbonate with various olefin polymers such as low density polyethylene or linear low density polyethylene, or thermoplastic rubbers such as ethylene/propylene copolymer These added substances are capable of improving the resistance of polycarbonate to solvents, but they tend to delaminate and cause an offsetting reduction in the toughness, impact resistance and weldline strength of the blended polycarbonate composition. Such delamination, and the resulting loss of utility, is reported, for example, in U.S. Pat. No. 4,496,693. In addition such polycarbonate/olefin polymer blends show high gloss, significant pearlescence, as well as solid opaque appearance.
In many automotive interior applications, such as instrument panel, head impact and interior trim, thermoplastic resins having good impact resistance, colorability and aesthetically pleasing attributes are essential.
Impact resistance in polycarbonate can be improved by the incorporation of emulsion or core-shell elastomers such as methacrylate/butadiene/styrene copolymer or a butyl acrylate rubber. However, these core-shell rubbers hinder processability of the blend by increasing viscosity. It would accordingly be desirable if modifers blended with polycarbonate for the purpose of improving its impact resistance did not also deleteriously affect its processability, and cause delamination as evidenced by peeling or splintering in a molded article.
The purpose of this invention is to provide novel blend compositions comprising one or more engineering thermoplastics and at least one substantially random interpolymer of one or more .alpha.-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.
The blend compositions can exhibit a unique balance of properties including high heat distortion temperature, excellent miscibility with no delamination and no pearlescence, excellent processability and good colorability when injection molded into various parts. In addition when the substantially random interpolymer component of the blend has high levels of vinyl or vinylidene aromatic monomer or hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer content (greater than about 36 mol %) then enhanced optical properties are observed including diminishing opacity and the generation of an almost translucent appearance in the fabricated part.
As a further embodiment, the invention provides novel blend compositions comprising one or more engineering thermoplastics, and at least one substantially random interpolymer of one or more .alpha.-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers in combination with one or more polyolefin elastomers and one or more ethylene-methyl acrylate-glycidyl methacrylate-styrene acrylonitrile multi polymer blends.
These blend compositions allow for the manufacture of PC/polyolefin compositions during extrusion which exhibit good low temperature toughness and impact strength and for which the processability and colorability is significantly improved via addition of one or more substantially random interpolymers of one or more .alpha.-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers. Such blend compositions additionally find utility in many automotive interior parts, involving, for example, instrument panel, head impact and interior trim applications.